feat(editor): admin-only raw HTML/CSS/JS embed node

Adds an htmlEmbed block node that renders and executes raw HTML/CSS/JS in the
wiki origin (e.g. an analytics tracker) — the owner-chosen variant C. Because
this is stored-XSS by design, only workspace admins/owners may get such a node
persisted; everyone executes it when reading.

- Node (editor-ext): htmlEmbed atom/isolating block; source stored base64 in
  data-source for lossless HTML<->JSON round-trip. renderHTML emits only the
  encoded marker (never inlines raw markup), so generateHTML/export/search are
  not themselves injection vectors. Registered in BOTH client extensions and
  server tiptapExtensions. Markdown round-trip via an <!--html-embed:b64-->
  comment (turndown) + a marked rule.
- Client NodeView: injects source and re-creates <script> elements so they
  actually run; edit modal; renders in read-only/share too. Slash item is
  admin-gated (adminOnly filtered by the user's workspace role).
- SERVER ENFORCEMENT (the real control — UI gating alone is insufficient):
  stripHtmlEmbedNodes() removes htmlEmbed from any document persisted by a
  non-admin, applied at every write path that introduces content from an
  untrusted author: collab onStoreDocument, REST/MCP/AI updatePageContent,
  single-file import, zip/multi-file import, page duplication, and transclusion
  unsync. Page restore introduces no new content. Public share/readonly viewers
  render fetched (already-stripped) content and do NOT open a collab socket, so
  the only residual is a transient broadcast window to concurrent authenticated
  editors (documented).

Implements docs/arbitrary-html-embed-plan.md (variant C).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/src/features/editor/components/html-embed/html-embed-view.tsx

@@ -0,0 +1,149 @@
+import { NodeViewProps, NodeViewWrapper } from "@tiptap/react";
+import React, { useCallback, useEffect, useRef, useState } from "react";
+import clsx from "clsx";
+import {
+  ActionIcon,
+  Button,
+  Group,
+  Modal,
+  Text,
+  Textarea,
+} from "@mantine/core";
+import { IconCode, IconEdit } from "@tabler/icons-react";
+import { useTranslation } from "react-i18next";
+import useUserRole from "@/hooks/use-user-role.tsx";
+import classes from "./html-embed-view.module.css";
+
+/**
+ * Inject raw HTML (including <script> tags) into `container`, executing any
+ * scripts.
+ *
+ * Setting `innerHTML` does NOT run inline or external <script> tags the browser
+ * parses that way: the HTML spec marks scripts inserted via innerHTML as
+ * "already started" so they never execute. To get the tracker/analytics
+ * use-case working we walk the freshly-parsed scripts and replace each with a
+ * brand-new <script> element copying its attributes and inline code. A
+ * programmatically created+inserted <script> DOES execute, so this restores
+ * normal script behaviour in the wiki origin (Variant C).
+ */
+function renderRawHtml(container: HTMLElement, source: string) {
+  // Clear any previous render (re-render on source change).
+  container.innerHTML = "";
+  if (!source) return;
+
+  container.innerHTML = source;
+
+  const scripts = Array.from(container.querySelectorAll("script"));
+  for (const oldScript of scripts) {
+    const newScript = document.createElement("script");
+    // Copy every attribute (src, type, async, defer, data-*, etc.).
+    for (const attr of Array.from(oldScript.attributes)) {
+      newScript.setAttribute(attr.name, attr.value);
+    }
+    // Copy inline code.
+    newScript.text = oldScript.textContent ?? "";
+    // Replacing the node in place triggers execution.
+    oldScript.parentNode?.replaceChild(newScript, oldScript);
+  }
+}
+
+export default function HtmlEmbedView(props: NodeViewProps) {
+  const { t } = useTranslation();
+  const { node, selected, updateAttributes, editor } = props;
+  const { source } = node.attrs as { source: string };
+  const { isAdmin } = useUserRole();
+
+  const contentRef = useRef<HTMLDivElement | null>(null);
+  const [modalOpen, setModalOpen] = useState(false);
+  const [draft, setDraft] = useState<string>(source || "");
+
+  // (Re)render the raw source whenever it changes. This runs in BOTH the
+  // editable editor and the read-only / public-share editor (same NodeView),
+  // so trackers fire for readers too — that is the intended behaviour.
+  useEffect(() => {
+    if (contentRef.current) {
+      renderRawHtml(contentRef.current, source || "");
+    }
+  }, [source]);
+
+  const openEditor = useCallback(() => {
+    setDraft(source || "");
+    setModalOpen(true);
+  }, [source]);
+
+  const onSave = useCallback(() => {
+    if (editor.isEditable) {
+      updateAttributes({ source: draft });
+    }
+    setModalOpen(false);
+  }, [draft, editor.isEditable, updateAttributes]);
+
+  // The edit affordance is only meaningful in edit mode, and authoring is
+  // restricted to admins (the server strips the node for non-admins anyway).
+  const canEdit = editor.isEditable && isAdmin;
+
+  return (
+    <NodeViewWrapper
+      data-drag-handle
+      className={clsx(classes.htmlEmbedNodeView, {
+        [classes.htmlEmbedSelected]: selected,
+      })}
+    >
+      {canEdit && (
+        <div className={classes.htmlEmbedToolbar}>
+          <ActionIcon
+            variant="default"
+            size="sm"
+            aria-label={t("Edit HTML embed")}
+            onClick={openEditor}
+          >
+            <IconEdit size={16} />
+          </ActionIcon>
+        </div>
+      )}
+
+      {source ? (
+        // Raw HTML/CSS/JS rendered into the wiki origin. Scripts are re-created
+        // in renderRawHtml so they execute.
+        <div ref={contentRef} className={classes.htmlEmbedContent} />
+      ) : canEdit ? (
+        <div className={classes.htmlEmbedPlaceholder} onClick={openEditor}>
+          <IconCode size={18} />
+          <Text size="sm">{t("Click to add HTML / CSS / JS")}</Text>
+        </div>
+      ) : (
+        // Empty source, non-editor: render nothing visible.
+        <div ref={contentRef} className={classes.htmlEmbedContent} />
+      )}
+
+      <Modal
+        opened={modalOpen}
+        onClose={() => setModalOpen(false)}
+        title={t("Edit HTML embed")}
+        size="lg"
+      >
+        <Text size="xs" c="dimmed" mb="xs">
+          {t(
+            "This HTML/CSS/JS runs in the page origin for everyone who views it. Admins only.",
+          )}
+        </Text>
+        <Textarea
+          autosize
+          minRows={10}
+          maxRows={24}
+          value={draft}
+          onChange={(e) => setDraft(e.currentTarget.value)}
+          placeholder={t("<script>...</script>")}
+          styles={{ input: { fontFamily: "monospace" } }}
+          data-autofocus
+        />
+        <Group justify="flex-end" mt="md">
+          <Button variant="default" onClick={() => setModalOpen(false)}>
+            {t("Cancel")}
+          </Button>
+          <Button onClick={onSave}>{t("Save")}</Button>
+        </Group>
+      </Modal>
+    </NodeViewWrapper>
+  );
+}